cc/gcc: add the backend/frontend infra for final gcc

Currently, we issue the bare-metal compiler from the pass_1 & pass_2
core compilers, because the final gcc breaks while doing so.

This implies we have to build some libces during the start_files step,
instead of the standard libc step. This is the case for newlib.

By adding a backend/frontend infra to the final gcc, we can abstract
what backend to call: the standard backend for non-bare-metal gcc,
and the core backend for bare-metal.

This patch is just an no-op, it just adds the final backend and
frontend without changing the way bare-metal is built, to come in a
subsequent patch.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 --- gcc-4.1.2.orig/gcc/Makefile.in	2006-11-01 15:40:44.000000000 +0100

 +++ gcc-4.1.2/gcc/Makefile.in	2007-03-04 23:34:32.000000000 +0100

 @@ -2522,7 +2522,7 @@

  # FIXME: writing proper dependencies for this is a *LOT* of work.

  libbackend.o : $(OBJS-common:.o=.c) $(out_file) \

    insn-config.h insn-flags.h insn-codes.h insn-constants.h \

 -  insn-attr.h  $(DATESTAMP) $(BASEVER) $(DEVPHASE)

 +  insn-attr.h  $(DATESTAMP) $(BASEVER) $(DEVPHASE) gcov-iov.h

  	$(CC) $(ALL_CFLAGS) $(ALL_CPPFLAGS) \

  	  -DTARGET_NAME=\"$(target_noncanonical)\" \

  	  -DLOCALEDIR=\"$(localedir)\" \